1. Field of the Invention
The present invention relates to a liner with which the interior of a manhole is lined (hereinafter called "manhole liner") and a method for lining a manhole with a manhole liner; and in particular the invention relates to a manhole liner impregnated with a thermosetting resin and a method for lining a manhole with such a liner.
2. Description of the Prior Art
When a manhole built in the ground becomes defective or too aged to perform properly, the manhole is repaired and rehabilitated without digging the earth to expose the manhole. This non-digging method of repairing an underground pipe has been known and practiced commonly in the field of civil engineering. Typically, the method is disclosed by European Patent Publication No. 0704294.
According to this publication, the method of manhole mending comprises: inserting into the manhole to be repaired a tubular manhole liner bag, which is made of a flexible resin-absorbable cloth material impregnated with a hardenable liquid resin and which has its outer surface hermetically covered with an impermeable polymeric film; inflating the liner bag to press it against the inner walls of the manhole by means of a fluid pressure or an inflatable pressure bag; and then curing the hardenable liquid resin to thereby harden the manhole liner bag, while the bag is closely pressed against the inner wall of the manhole. It is thus possible to line the inside wall of the defective or aged manhole with a rigid liner.
Incidentally, the above-mentioned inflatable pressure bag is inserted into the manhole liner bag in the following manner: the open end of the pressure bag is made to gape wide and hooked (anchored) at the upper open end of the manhole in a manner such that the wide-opened end of the pressure bag completely and fixedly covers and closes the upper open end of the manhole; a portion of the pressure bag is pushed into the manhole whereby an annular pocket is made; then, a pressurized fluid is applied to the pocket portion of the pressure bag such that the fluid urges the pressure bag to enter the manhole. Since one end of the pressure bag is hooked at the upper end of the manhole, it remains there while the rest of the pressure bag proceeds deeper into the manhole as it is turned inside out. (Hereinafter, this manner of insertion shall be called "everting" nor "eversion".)
Before lining the manhole with the liner bag in the above-mentioned method, however, a plurality of ladder steps, which are rigidly fastened to the inner wall of the manhole in a descendent row, must be removed, and when the manhole has been newly lined with the liner bag, holes are made at intervals through the rigid liner from inside the manhole and these holes extend partially into the wall of the manhole, and, then, a plurality of new ladder steps are hit in these holes and fastened therein.
However, if the manhole is very aged, the manhole wall is so fragile that the steps rooted in it cannot be reliably steady, and may fail to bear the weight of a man stepping on them. Hence, the applicant submitted a patent application (Japanese Patent Application No. 8-62735) wherein it is proposed that the ladder steps are supported by the manhole liner via step connector assemblies, rather than by the manhole wall.
More particularly, this proposal, as illustrated in FIG. 13, teaches that each step connector assembly includes bolts 108, which are supported by the rigid manhole liner 103 and partially extend beyond the inner face of the manhole liner 103. The step connector assembly further includes a pair of vertical plates 105, which are laid over the outer face of the manhole liner 103 and with which the heads of the bolts 108 are integrally formed. A plurality of such step connector assemblies to receive ladder steps are arranged in a row extending in the direction of the depth of the manhole liner bag 101. Then, as shown in FIG. 14, the manhole liner bag 101 provided with these step connector assemblies is inserted into a manhole 121 and hardened to fit on the inner wall of the manhole 121; next, an attachment plate of a ladder step 114 is engaged with the bolts 108, which are extending beyond the inner face of the liner 103, followed by screwing of nuts 109 on the threaded ends of the respective bolts 108 until the ladder step 114 is firmly supported by the manhole liner 103. Incidentally, in the case of FIG. 14, a plate is provided between the liner 103 and the step 114.
Thus, as a result of the above-described method, even in a case where the manhole 121 was so aged that the wall of the manhole was too fragile to hold steps on its own, it was possible to attach the ladder steps 114 with sufficiently high steadiness so that the steps would not totter when a person climbs them. Also, by virtue of the pre-installed bolts extending beyond the inner face of the manhole liner, the ladder steps could be easily attached to the liner, and it was unnecessary to make holes into the inner wall of the hardened liner for attachment of the ladder steps. Hence, the human labor at the site was much reduced and the operation time was substantially shortened.
(Problems the Invention seeks to solve)
However, in the above-described method, the bolts 108 protruded from the inner face of the manhole liner bag 101, and when an inflatable pressure bag 135 was everted into the manhole liner bag 101 after the latter had been inserted into the manhole 121, the pressure bag 135 is liable to be scratched by the bolts 108, as shown in FIG. 15, and as a result the pressure bag 135 burst occasionally; also, another problem was that the uncured hardenable liquid resin impregnated through the manhole liner 103 tended to permeate along the external threads of the bolts 108 and harden to clog the thread groove so that it sometimes became impossible to screw the nuts 109 on the bolts 108.
In an attempt to solve this problem, it was proposed to seal the threaded ends of the bolts 108 of the step connector assembly with caps 130 held by rubber plate 129, as shown in FIG. 16; however, even in this method, the uncured hardenable liquid resin impregnated through the manhole liner 103 continued to ooze along the external threads of the bolts 108 and harden so that it was sometimes impossible to screw the nuts 109 on the bolts 108, when the steps 114 were attached to the manhole (ref. FIG. 14).